What is the Application Server?
The Application Server provides a robust J2EE platform for the development, deployment, and management of enterprise applications. Key features include transaction management, performance, scalability, security, and integration. The Application Server supports services from Web publishing to enterprise-scale transaction processing, while enabling developers to build applications based on JavaServer Pages (JSP), Java servlets, and Enterprise JavaBeans (EJB) technology.
The Application Server Enterprise Edition provides advanced clustering and failover technologies. These features enable you to run scalable and highly available J2EE applications.
- Clustering - A cluster is a group of application server instances that work together as one logical entity. Each Application Server instance in the cluster has the same configuration and the same applications deployed to it. The Application Server instances within a cluster can span different machines into one logical cluster.
Scaling is acheived by adding Application Server instances to a cluster and
thereby increasing the capacity of the system. It is possible to add Application
Server instances to a cluster without disrupting service. The HTTP and
RMI/IIOP load balancing system distributes requests to healthy Application
Server instances in the cluster.
- Load Balancing - Balancing is achieved by evenly distributing the workload among multiple physical machines and thereby increasing the throughput of the overall system. The Application Server load balancer plugin can be configured for application requests along with HTTP, HTTPS, and IIOP requests. The plugin forwards them to one of the application server instances in the cluster.
- High Availability - Availability allows for failover protection of Application Server instances in a cluster. If one application server instance goes down, another Application Server instance takes over the sessions that were assigned to the unavailable server. Session information is stored in the high-availability database (HADB). HADB supports the persistence of HTTP sessions, EJB stateful session beans, and remote references of EJB lookups on the RMI/IIOP path.
- Session Persistence - Session persistence ensures that if an Application Server instance fails, the HTTP/S or EJB session is picked up by another server instance. The Application Server supports persistence of the following:
- HTTP sessions
- EJB references within HTTP sessions
- Stateful Session Beans (SFSB)
The high-availability database functions as the persistence store and consists of two Data Redundancy Units (DRUs) which are logical groupings of nodes. A DRU contains active and spare nodes. An active node stores data. If an active node becomes unavailable, a spare node takes its place. So, each active node must have a mirror active node on the other DRU.
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